Energy shortages have precipitated research and development of more and more efficient systems for processing and conditioning the air in an enclosure. Initially, systems having the capability to service multiple thermal zones replaced systems wherein each zone was conditioned by a separate heating, ventilating and air conditioning unit (hereinafter HVAC unit). One widely accepted multizone system (hereinafter the Gilles system) is fully described in U.S. Pat. No. 3,927,713, and its teachings are incorporated herein by reference. The present case and U.S. Pat. No. 3,927,713 have a common assignee.
The Gilles system is a constant air volume system. That is, the air mover delivers processed supply air to each zone at a constant rate, e.g., 2000 cfm.
The coldest and hottest zones receive supply air primarily from the hot and cold decks, respectively, of the HVAC unit. The zones of intermediate temperatures receive a combination of hot and cold deck supply air, effected by dampers responsive to a thermostat within the particular zone. The dampers are rigidly secured together in a perpendicular arrangement.
Multizone variable air volume systems (hereinafter VAV systems) were developed to overcome the inherent shortcomings of the constant air volume multizone systems, including the Gilles system. In particular, the VAV systems avoid, under certain conditions, the mixing of hot and cold deck supply air to process the intermediate zones. This mixing is wasteful and avoidance thereof provides the potential for substantial energy savings.
Unfortunately, the presently available VAV systems have certain disadvantages not found in the Gilles system. The VAV systems do not have heat reclaim capability, without expensive additional equipment; morning warmup, particularly after weekend shutdown periods, is slow and inefficient; under certain operating conditions, supply air must be substantially cut off to avoid reheat characteristics, virtually eliminating fresh air ventilation of the zone; and further, separate perimeter zone heating units are often required.